Got Win 7 32 bit and I have roughly the same problem. The game freezes after about 1-2 seconds at the menu then I have to ctrl+atl+del so I can at least see the "Hey.... this game has crashed" window.

EDIT::
It dawned on me that it could very well possibly be the Steam overlay (since that's the same time frame that the overlay pops up telling you that you can use it)... sure enough it is. If anyone else is having this problem just go into your Steam folder and look for the Defcon folder (..Steam\steamapps\common\Defcon) and run the .exe from there. As I type this the game is alt+tab'd - which works fine btw.